Screw fan



Sept. 22, 1942.

A. L. MlLLAR SCREW FAN Filed July 51, 1941 Patented Sept. 22, 1942 OFFICE SCREW FAN Arthur Lansworth Millar, London, England Application July 31, 1941, Serial No. 404,921 In Great Britain May 4, 1940 1 Claim.

This invention relates to improvements in and connected with fans, and is principally applicable to circulatory and exhaust fans. This invention comprises broadly a fan for rotation in compressible fluids adapted to create or move a current of air by virtue of its rotation from reactions due to separating relative flows over the blades in at least one sense of direction. The following describes a manner of developing a fan according to my invention.

The leading edge is straight, and lies substantially in a plane of rotation, and may also lie in a diameter through the centre of the shaft. In a two bladed fan, tips of opposed blades may lie in the same diameter or may be offset. The trailing edge passes in a straight line from its junction with the boss at an angle of about 30 with the leading edge When viewed in the fiat, outwards, divergent to the leading edge, curving around opposite the greatest width of the blade, and straightening out towards the tip of the blade, meeting the leading edge at an angle of 60 or thereabouts. Radially the trailing edge lies wholly in the same plane. Both leading and trailing edges are also in a plane at an angle to the plane of rotation about the shaft axis. The width of the blade increases towards the tip, and the radial dimension is greatest in the plane of the leading edge. The root of the blade may be attached to the boss at an angle to the axis of the shaft, so that if the extremities of the leading and trailing edges were prolonged to the centre of the boss, they would meet at the centre at an angle of 30 or thereabouts. The working face may be a fiat surface, or may be concave or partly concave in an axial and radial direction, both concavities being most marked where the blade is widest. The working face may pass in a flat plane rearwardly from the leading edge, and at a varying distance from its commencement, curve in the remainder of its length, or the working face may axially be concave from the leading edge, and at a varying distance from its commencement straighten outin the remainder of its length. Radially the following face may be convex, the summit of the convexity being opposite the greatest width of the blade, or the following face radially may be straight from its attachment to the boss, becoming convex at the widest part of the blade and towards the tip. Radially the following face may be convex, straightening out towards the tip. Axially the following face may be convex, or may straighten out towards the trailing edge. The following face may end in a sharp ridge at either extremity of the blade.

A cross-section of the blade is preferably cambered in outline. The following and working faces may meet at a sharp margin at the leading and trailing edges. The boss may be cylindrical and of suitable thickness and length, and the root of the blade may be attached to the front or rear end of the boss. The fan may consist of one or more blades.

According to the present invention a blade for a fan has a straight leading edge, adapted to lie substantially in the plane of rotation of the blade, the trailing edge of the blade at the root forming an angle with the leading edge when viewed in front elevation so that if the extremities of the leading and trailing edges were prolonged to the centre of the boss, they would meet at the centre at an angle, whilst the outer end of the trailing edge is connected by a curve to a straight line which meets the leading edge at an angle of about The root of the blade may be connected to a boss at an angle to the axis of the boss. The following face of the blade is convex or partly convex, whilst the working face may be flat or concave, or partly flat and partly concave in a radial and in an axial direction. When two blades are secured to a boss, the leading edges of the two blades may be arranged along a diameter of the boss, or the leading edges may be slightly offset relatively to one another. In the case of three or more blades, the leading edges are uniformly spaced around the boss, and may all lie in the same plane.

The invention will now be described by Way of example with reference to the accompanying drawing, wherein:

Figure 1 is a front view of a two-bladed fan;

Figure 2 is a section on the line A, B, C, of Figure 1; and

Figure 3 shows cross-sections of a blade at different points along its length.

As shown in Figure 1, a blade I is provided with a straight leading edge 2, this edge being shown located on a diameter passing through the centre of a boss 3. The leading edge 2 lies substantially in the plane of rotation of the fan. The leading edges 2 of the two blades 1 are located in the same plane. The trailing edge 4 is arranged at an angle of about 30 to the leading edge 2 as shown in Figure 1 if projected to meet the leading edge at the centre of the boss. At its outer end the trailing edge 4 passes with a curve 5 into a straight portion 6 which meets the leading edge at its tip 1 at an angle of about 60.

The leading edges 2 of the blades I extend at right angles to the axis of the boss 3.

The roots 8 of the blades I are secured to the boss 3 at an angle so as to bring the leading edges 2 in advance of the trailing edges 4 when looking at Figure 1. The Working face 9, Figure 3, passes in a flat plane rearwardly from the leading edge 2, and at a varying distance from this edge curves to the trailing edge, the concave shape being at its maximum at the widest part of the blade.

The following face I in a radial direction is convex, the summit of the convexity being on the line of greatest width of the blade I and being opposite the maximum concavity of the working face.

In the axial direction the following face is entirely convex.

The leading and trailing edges 2, 4, are sharp.

The boss 3 may be cylindrical and the blade 0r blades secured thereto ator near the front or rear end thereof.

I claim:

A blade for a fan, the said blade having a straight leading edge, adapted to lie substantially in the plane of rotation of the blade, the trailing edge of the blade at the root forming an angle of about with the leading edge when viewed in front elevation, the leading and trailing edges if projected intersect the axis about which the fan rotates, whilst the outer end of the trailing edge is connected by a curve to a straight line which meets the leading edge at an angle of about the following face of the blade being approximately convex, and the working face of the blade bein partly fiat and partly concave in a radial and in an axial direction.

ARTHUR MNSWORTH MILLAR. 

